1. Field of the Invention
The present invention relates to plasma process apparatuses, and more particularly, to a plasma process apparatus for use in fabrication of a semiconductor device, a liquid crystal display device or the like.
2. Description of the Background Art
Conventionally, a plasma process apparatus with a capacitively-coupled plasma source has been utilized for fabricating a semiconductor device, a liquid crystal display device or the like, in which a pair of electrodes are placed within a process chamber and supplied with high-frequency power of 13.56 MHz as means of plasma excitation. In such an apparatus, an object being processed is placed on one of the electrodes. If the object being processed is conductive, it is possible to excite plasma using direct-current (DC) power even with such a capacitively-coupled type apparatus.
Recently, in an effort to realize a more advanced, highly productive device fabrication technique, a plasma process apparatus incorporating a plasma source capable of exciting so-called xe2x80x9chigh density plasmaxe2x80x9d has been developed extensively. Although plasma exciting means based on a variety of principles can be employed for such an apparatus, the one utilizing microwave is highly advantageous. When employing the microwave, besides the fact that the high density plasma as mentioned above can be obtained, it becomes unnecessary to provide a process chamber with an electrode for introduction of power necessary at least for plasma excitation. This eliminates a possibility of contamination of impurities associated with the electrode material. In addition, the plasma excited with the microwave has a potential that is lower than the plasma obtained by the capacitively-coupled type apparatus, which leads to another advantage that influx of energy particles to the surface of the object being processed can be controlled to a greater extent.
With conventional apparatuses, however, it has been difficult to realize a plasma state that permits uniform processing of a relatively wide area. A number of techniques have been proposed to address this problem.
One of the techniques is disclosed in Japanese Patent Laying-Open No. 11-111493. FIGS. 16 and 17 schematically show vertical and horizontal cross sectional views, respectively, of a plasma process apparatus disclosed therein.
Referring to FIGS. 16 and 17, the plasma process apparatus includes, among others, a reaction chamber 120, a microwave introduction window 102, a stage 107, a dielectric line 111, a microwave distributor 113, a microwave waveguide 114, and a microwave oscillator 115.
The inside of metal reaction chamber 101 constitutes a reaction chamber 120, whose top is sealed airtight by microwave introduction window 102. Within reaction chamber 120 a stage 107 is placed for holding thereon a semiconductor substrate 108 as an object being processed. A high-frequency power supply is connected to stage 107. Four partitioned dielectric lines 111 are provided above microwave introduction window 102, with a prescribed spacing (air gap 112) provided therebetween. An outer periphery of each dielectric line 111 is covered with a metal plate 116. Each dielectric line 111 has its side connected to microwave waveguide 114 via microwave distributor 113. Microwave oscillator 115 is attached to the end of microwave waveguide 114.
In the operation of this apparatus, the interior of reaction chamber 120 is first evacuated down to a required level of pressure, followed by introduction of reaction gas therein via a gas feed tube. Microwave are then oscillated at microwave oscillator 115, which are led via waveguide 114 to microwave distributor 113.
The microwave divided at microwave distributor 113 are led to respective dielectric lines 111 in phase with the same power. The microwave led to dielectric lines 111 pass through air gap 112 and introduced into reaction chamber 120 via microwave introduction window 102. With the introduction of the microwave, plasma is produced within reaction chamber 120, whereby plasma processing (etching) is applied on the surface of substrate 108 placed on stage 107.
Other techniques to realize uniform plasma processing in a relatively wide area are disclosed, e.g., in Japanese Patent Laying-Open No. 8-316198, Japanese Patent Publication No. 7-105385 and Japanese Patent No. 2641450.
Japanese Patent Laying-Open No. 8-316198 discloses a plasma process apparatus wherein microwave oscillated by a single microwave oscillator are branched and transmitted via a plurality of dielectric layers into a reaction chamber.
Japanese Patent Publication No. 7-105385 discloses a plasma process apparatus wherein a plurality of waveguides are connected to the upper part of a process chamber, and a plurality of microwave oscillators are respectively connected to the waveguides, whereby a plurality of microwave are controlled independently from each other.
Japanese Patent No. 2641450 discloses a plasma process apparatus that is similar to the one disclosed in Japanese Patent Publication No. 7-105385 in that each waveguide requires a respective set of microwave oscillator. The difference therebetween is only the way of plasma excitation.
Microwaves generally refer to electro-magnetic waves of frequencies of 1-30 GHz. However, in the field of engineering, waves of VHF band (30-300 MHz), UHF band (0.3-3 GHz) and milliwave band (30-300 GHz) can be handled in the same manner as the microwaves of the general definition. Hence, in this specification, the electromagnetic waves of these frequency bands are collectively referred to as the microwaves.
The techniques disclosed in the references above have disadvantages as follows.
First, in the plasma process apparatus of Japanese Patent Laying-Open No. 11-111493 as shown in FIGS. 16 and 17, microwave in phase with the same power are introduced into four partitioned dielectric lines 111. Of microwave introduction window 102, however, in a region SA that is closer to a sidewall 101b of reaction chamber 101 and in a region SB farther from the sidewall 101b, there are differences in the potential states and in the manners of excited particle generation/dissipation within the plasma. Accordingly, load impedance of the plasma immediately beneath the region SA differs from that beneath the region SB, thereby hindering a uniform plasma process.
In the plasma process apparatus of Japanese Patent Laying-Open No. 8-316198, the dielectric layer is partitioned only into two parts. This is insufficient for uniformly processing a substrate of wide area. Even if the number of partition of the dielectric layer is increased, load impedance differs in different positions as in the case of Japanese Patent Laying-Open No. 11-111493, which again hinders the uniform plasma process.
In Japanese Patent Publication No. 7-105385 and Japanese Patent No. 2641450, one microwave oscillator is required for a respective waveguide. In general, it is more advantageous from the standpoint of cost saving to prepare, instead of a plurality of oscillators each of low power level, one powerful oscillator capable of supplying the equivalent power. Accordingly, the apparatuses disclosed in these references are disadvantageous in terms of cost saving, and will become more disadvantageous if they are to be used to process a substrate of large area.
An object of the present invention is to provide a cost-effective plasma process apparatus that allows a uniform plasma process even if plasma produced within a reaction chamber exhibits different load impedance in different positions.
The plasma process apparatus according to the present invention applies a plasma process on a substrate employing reaction gas that has been excited to a plasma state by microwaves. The plasma process apparatus includes a chamber and a plurality of microwave introduction windows. With a substrate held therein, the chamber has a main wall facing the surface of the substrate and a sidewall surrounding the side of the substrate. The plasma process is performed within the chamber. The plurality of microwave introduction windows are provided at the main wall to face the interior of the chamber for introduction of the microwaves into the chamber. Of the plurality of microwave introduction windows, at least two microwave introduction windows that are equivalent in location relationship with respect to the sidewall are supplied with microwaves of essentially identical power. At least two microwave introduction windows that are non-equivalent in location relationship with respect to the sidewall are supplied with microwaves of different power.
In the plasma process apparatus of the present invention, microwaves of different power are introduced into microwave introduction windows that are non-equivalent in location relationship. Accordingly, it becomes possible to make the plasma states immediately beneath the respective microwave introduction windows approximately identical to each other even if load impedance of the plasma beneath those windows differs from each other.
Load impedance of the plasma immediately beneath the microwave introduction windows that are equivalent in location relationship should be essentially identical to each other. Thus, microwaves of the same power are introduced into these microwave introduction windows, thereby controlling the plasma states beneath the windows to become substantially identical to each other.
The plasma can thus be made to have a uniform plasma state throughout the entire chamber, and therefore, it becomes possible to apply a uniform plasma process on a substrate of large area.
Microwave are led to the microwave introduction windows that are equivalent in location relationship using a single, powerful microwave oscillator, which is advantageous in cost saving.
With the plasma process apparatus as described above, when the plasma generated within the chamber is expressed as equivalent loads of parallel lumped-constant circuits, the plasma generated by microwave introduced from at least two microwave introduction windows equivalent in location relationship has load impedance essentially identical to each other.
In this manner, the microwave are supplied taking into consideration even the load impedance of plasma being generated within the process chamber. This enables a more uniform plasma process.
Preferably, the plasma process apparatus is further provided with a microwave waveguide for transmission of microwaves. One such microwave waveguide is branched and connected to respective ones of at least two microwave introduction windows that are equivalent in location relationship.
One microwave oscillation source is connected to this single microwave waveguide, so that it becomes possible to introduce microwaves to respective microwave introduction windows that are equivalent in location relationship using one powerful microwave oscillation source.
Preferably, the plasma process apparatus is further provided with a microwave oscillation source for oscillation of microwaves. One such microwave oscillation source is connected to the one microwave waveguide.
Thus, it becomes possible to achieve a cost-effective plasma process apparatus.
Preferably, the plasma process apparatus is further provided with a microwave waveguide for transmitting microwave, and an attenuator that can adjust an amount of attenuation of the microwave. One such microwave waveguide is branched and connected to respective ones of at least two microwave introduction windows that are non-equivalent in location relationship. One such attenuator is connected to a respective branched portion of the microwave waveguide.
Thus, it becomes possible to introduce microwaves even to the microwave introduction windows that are non-equivalent in location relationship using a single, powerful microwave oscillator. Accordingly, a still more cost-effective plasma process apparatus can be achieved.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.